1. Field of the Invention
This invention relates to a process for producing a cyclic ether in a single step from an acetic ester of a glycol and, in more particular, to a process for producing tetrahydrofuran or dihydrofuran from an acetic ester of 1,4-butanediol or 1,4-dihydroxybutene-2.
2. Description of Prior Art
Tetrahydrofuran is useful as a solvent for polymeric materials, such as polyvinyl chloride and polyvinylidene chloride, and is produced by various processes; for example, catalytic hydrogenation of furan produced by decarbonylation of fulfural; reacting acetylene and formaldehyde to obtain butynediol, followed by hydrogenation and dehydrocyclization to produce tetrahydrofuran, and reacting diacetic ester of 1,4-butanediol with water in the presence of an acid catalyst (refer to British Patent 1,170,222).
From an extensive study of producing a cyclic ether, especially tetrahydrofuran, from an acetic ester of a 1,4-glycol, I have found that, if the raw material acetic ester is contacted with steam in stoichiometrically excess amount and in a liquid-gas countercurrent contact, the conversion of the acetic ester into a cyclic ether is improved and, at the same time, the desired product is readily recovered as a gaseous material from the reaction system.
I have also found that, since tetrahydrofuran and water form an azeotropic mixture, the use of an excess amount of water requires repeated distillation steps for recovering anhydrous tetrahydrofuran from the reaction product. On the other hand, if the amount of water is decreased, the conversion will lower to make the process uneconomical.
In order to obtain a reaction product containing the desired cyclic ether in high content without lowering the conversion and to recover a high quality cyclic ether by simple distillation procedure, I have conducted further investigation to find that a high quality cyclic ether substantially free from water is obtained by effecting the reaction in a plurality of reaction zones and recycling a part of the reaction product to a predetermined reaction zone. This invention has been accomplished on the basis of the above knowledge.